1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device, and particularly to a semiconductor device with a lateral high breakdown voltage element and a method for manufacturing such a semiconductor device.
2. Description of the Background Art
As a semiconductor device with a lateral high breakdown voltage element, a driver circuit for operating a load such as an induction motor or the like will be described. A drive control circuit includes a low-side circuit that controls switching operation of a semiconductor device such as an IGBT (Insulated Gate Bipolar Transistor) or the like, using a substrate potential as a reference, a high-side circuit that controls switching operation of the semiconductor device using a prescribed potential (high voltage) higher than the substrate potential as a reference, and a level shift circuit that transmits a signal between the high-side circuit and the low-side circuit.
The high-side circuit is electrically isolated from the low-side circuit. Structurally, by way of a high breakdown voltage isolation region formed to surround a periphery of a high-side circuit region where the high-side circuit is formed, the high-side circuit region and a low-side circuit region where the low-side circuit is formed are electrically isolated from each other.
The high breakdown voltage isolation region electrically isolates the substrate potential and the high voltage by utilizing a resurf structure (effect). That is, in the high breakdown voltage isolation region, the impurity concentration of an N type impurity region (CN) and the thickness (d) of the impurity region are so set to satisfy a resurf condition (CN×d≦prescribed concentration). Non-patent document 1 (J. A. Appels and H. M. J Vaes “High voltage thin layer devices (RESURF devices)” IEDM, pp 238-241 1979.) and non-patent document 2 (J. A. Appels, M. G. Collet, P. A. H. Hart, H. M. J. Vaes and J. F. C. M. Verhoeven “Thin layer high-voltage devices (RESURF devices)” Philips J. Res. 35, 1-13, 1980.) can be mentioned as examples of documents that disclose resurf structures.
When, for example, a rectangular pattern is employed as the layout pattern of the high-side circuit region, the high breakdown voltage isolation region extends linearly (linear portion) in a section of the pattern extending linearly, and has a fan shape at corners of the pattern (corner portion). The high breakdown voltage isolation region is thus constituted of the linear portion and the corner portion.
Conventionally, in the high breakdown voltage isolation region, the impurity concentration in the linear portion and the impurity concentration in the corner portion are set to be the same.